Entomological investigation and distribution of Aedes mosquitoes in Tirunelveli, Tamil Nadu, India

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International Journal of Current Microbiology and Applied Sciences ISSN: 2319-7706 Volume 3 Number 10 (2014) pp. 253-260 http://www.ijcmas.

1 International Journal of Current Microbiology and Applied Sciences ISSN: Volume 3 Number 10 (2014) pp Original Research Article Entomological investigation and distribution of Aedes mosquitoes in Tirunelveli, Tamil Nadu, India Mohd. Ayoub Bhat * and K. Krishnamoorthy Division of Epidemiology and Operational Research, Vector Control Research Centre, Indian Council of Medical Research, Indira Nagar, Pondicherry, India *Corresponding author A B S T R A C T K eywo rd s Entomological study; Aedes mosquitoes; Breeding sources; Larval indices; Adult density based indices; Tirunelveli. Entomological survey was carried out extensively (covering the large areas) following the major dengue outbreak (2012) in Tirunelveli district of Tamil Nadu. The study was performed to investigate the various breeding sources and distribution dynamics of dengue vectors. Different technique indices were integrated in this study to understand the significance of entomological surveillance in maintaining the populations of dengue vectors. The most common storage containers used by the residents of Tirunelveli were plastic drums, cement tanks, plastic containers and aluminum utensils which were found the major breeding sources in Tirunelveli. The larval indices like house index, container index, breteau index, and pupal index varied from , , and respectively. The pupae/container and pupae per positive container varied from and Adult female Aedes mosquitoes were collected from the same selected premises as those studied during the larval survey and various adult density based indices were calculated. The adult premise index varied from whereas females per house inspected and females per positive house (for Aedes mosquitoes) varied from and respectively. The study showed that the three species of Aedes mosquitoes (both immatures and adults) were abundantly distributed and expanded their range in all the study areas of Tirunelveli District. Introduction The vector borne diseases (VBDs.) mostly the mosquito borne diseases (MBDs.) have become important world health problems because there is no vaccine or drug available against these diseases so for. These diseases are standing as the potential risks to the major population of the world. Nowadays dengue fever, one of the mosquito borne diseases, has created havoc to all over world. It is an acute febrile illness and crucial public health problem. It has been reported that 2.5 billion people are at risk globally and this disease is found all over the world (Fradin et al., 2002). Every year newer areas of the world are invaded by this dreadful dengue infection. The disease may cause hemorrhages and plasma leakage giving birth to fatal diseases; the dengue hemorrhagic fever (DHF) 253

2 and dengue shock syndrome (DSS) respectively (WHO, 1997) which are the main causes of infant mortality (Monath et al., 1994). In India, DF and DHF has knocked the doors of many different parts of the country (Agarwal et al., 1996) including southern India (Kabilan et al., 2003; Victor et al. 2007). Among 30 districts of Tamil Nadu, 29 districts were found infected with dengue infections which includes DHF outbreaks in Chennai (Kabilan et al., 2003), Dharmapuri (Victor et al., 2002), Tiruchirappalli (Rajesh et al., 2013) and Virudhunagar district (Wilson et al., 2014). It was reported in daily newspaper, The Hindu (dated; 15 July 2012) that a total 9,000 cases and 50 deaths were reported in districts of Madurai, Tirunelveli and Kanyakumari. Although Aedes aegypti, the principal vector (WHO, 2003) is extensively distributed in many towns and cities of India (Sharma et al., 2000; Tandon et al., 2000), the dengue virus has also been detected in Ae. Albopictus (Das et al., 2004). The various meteorological factors like temperature, rainfall and humidity affect the distribution of Aedes mosquitoes and the dengue infection generally become apparent during or after rainfall, as an outcome of rise in vector population (Pandya, 2014). Entomological survey was carried out extensively following the major dengue outbreak (2012) in Tirunelveli district of Tamil Nadu. The study was performed to investigate the various breeding sources and distribution dynamics of dengue vectors. Different technique indices were integrated in this study to understand the significance of entomological surveillance in maintaining the populations of dengue vectors. Materials and methods The entomological survey was carried out (from September 2013 December 2013) extensively (covering large areas) following the major dengue outbreak (2012) in Tirunelveli district of Tamil Nadu. The study was performed in randomly selected houses in 12 different areas of Tirunelveli Tamil Nadu, India (namely Puliankudi, Sankarankiol, Tenkasi, Ramaiyanpatti, Marathamputhur, Chettiyur, Shenkottai, Sivagiri, Alangulam, Panaagudi, Surandai and Vellanguli) (Fig. 1). Various breeding sources and distribution dynamics of Aedes mosquitoes was operated in our study. Tirunelveli district is located 700 km to the southwest of the state capital, Chennai and covers an area of km 2. It is situated at N and E with an average elevation of 47 meters. The climate of Tirunelveli is generally hot and humid with an average annual rainfall of 680 millimeters. Larval Collection All kinds of indoor and outdoor breeding habitats were examined to collect the Aedes immatures by following the dipper method (Reuben, 1978). A container containing any amount of water was considered as wet container and the wet container containing any number of immatures (larvae, pupae or both) was considered as positive container. The immatures were collected by using different immature collecting materials like pipettes, dipper, strainer depending upon the type and size of breeding source. The collected immatures were kept in plastic containers labeled with the code of breeding source, locality code, house identification code and date of collection. The samples were carried to the laboratory in Vector Control Research Centre (VCRC), Pondicherry. The immatures (larvae and pupae) were counted and reared in enamel trays for their emergence into adults. Every day the emerged mosquitoes were collected and identified according to species and sex. In this way species composition and sex ratio of emerged 254

3 mosquitoes was calculated. The larval survey data was calculated and analyzed in terms of different larval survey techniques like House Index (HI), Container Index (CI), Breteau Index (BI), Pupal Index (PI), Pupae Per Container Index (PCI) and Pupae Per Positive Container Index (PPCI) according to various methods (WHO, 2003; Service, 1976). The calculation of larval indices is based on the following mathematical formulae: House Index (HI) = Number of houses infested/total number of houses inspected multiplied by 100. Container Index (CI) = Number of positive containers infested/total number of containers inspected multiplied by 100. Breteau Index (BI) = Number of positive containers/ Total number of houses inspected multiplied by 100. Pupal Index (PI) = Number of pupae collected/total number of houses inspected multiplied by 100. Adult collection Adult female Aedes mosquitoes were collected from the same selected premises as those studied during the larval survey. The collection of female Aedes mosquitoes was performed by following the standard protocol (Sundeep et al., 2009 and Chan et al., 1971). Both indoor and outdoor resting places were explored to collect the female adult Aedes mosquitoes using mechanical/oral aspirators and flash torch was used to locate the resting places of mosquitoes from dark areas. The collected adult mosquitoes were stored in plastic vials labelled with locality code, house identification code and date of collection. The adult density was calculated by means of Adult Premise Index (API, number of positive houses for adult female Aedes mosquitoes divided by the number of inspected houses multiplied by 100); Adults Per House (number of female adult Aedes mosquitoes collected divided by houses inspected); Adults Per Positive House (number of collected adult female Aedes mosquitoes per positive house for Aedes mosquitoes). Adult identification The collected and emerged adults were pinned and identified under microscope to separate them according to species and sex by using the standard taxonomic keys (Tyagi et al., 2012; Barraud & Philip James, 1934). Adult Aedes mosquitoes were identified by the exposed patterns of the thorax formed by black, white or silvery scales and the legs were often black with white rings. The Ae. aegypti is identified by the presence of mesonotum marked with a pair of lateral curved white lines usually with a pair of sub median yellowish line. The tibia is without rings and clypeus consists of two dots of white scales. Another dengue vector; Aedes albopictus is identified by the presence of narrow median silvery white line in mesonotum. The pleurae were arranged in irregular patches with white lines and tibia is without white line. The Aedes vittatus, another species collected from the study areas was identified due to the presence of 4-6 small white spots on the mesonotum and having tibiae with white rings. Results and Discussion Total of 550 houses were surveyed from 18 residential areas (Table 1) and 107 houses were had positive breeding sources for Aedes mosquitoes. Both artificial and natural breeding sources were examined. Out of 3778 containers screened 150 containers were found to support the Aedes mosquito breeding (Table 1). On the basis of positive houses and positive containers observed, the various larval indices were calculated to determine the distribution dynamics of Aedes species and to detect the dengue prone areas. In our study the 255

4 HI, CI, BI, and PI varied from , , and respectively (Table 1). The indices related to the pupal production other than pupal index (PI) like the pupae/container and pupae per positive container varied from and (Table 2) and thus depending on the size and material of breeding source, the pupal productivity fluctuates which was also observed from American studies (Burkot et al., 2007). The major breeding sources (Table 2) observed were Cement tanks 17 (4.79%) followed by Plastic drums 13 (4.36%), Tyres 2 (2.56%), Grinding stones 3 (2.29%), Plastic containers 10 (2.18%), Aluminium utensils 10 (1.76%), Flower pots 1 (1.10%). Plastic buckets and Iron pots were not found positive for breeding. Similar studies have also been conducted in Tiruchirappalli (Rajesh et al., 2013) and Virudhunagar (Wilson et al., 2014) districts of Tamil Nadu, India. As all the collected immatures were reared and allowed to emerge into the adults, the composition of emerged species consisted of three species of Aedes mosquitoes; Aedes aegypti 281 (49.13%), Aedes vittatus 224 (39.16%) and Aedes albopictus 67 (11.71%) (Fig 2 and Table 3). Similar results were obtained in other studies conducted in Tiruchirappalli (Rajesh et al., 2013) and Virudhunagar (Wilson et al., 2014) districts of Tamil Nadu, India. Table.1 Larval indices and distribution of Aedes mosquito breeding habitats at different locations in Tirunelveli district Location Total houses Positive houses Total containers Positive containers Pupae HI CI BI PI Puliankudi Sankarankoil Tenkasi Ramaiyanpatti Maruthamputhur Chettiyur Shenkottai Sivagiri Alangulam Panaagudi Surandai Vellanguli Total HI-House Index, CI-Container Index, BI-Breteau Index, PI- Pupal Index. Table.2 Container positivity and pupal indices Container type No. of containers No. of Positive Container No. of pupae Pupae/positive examined containers positivity collected Pupae/container container Coconut shells Cement tanks Plastic drums Plastic containers Plastic buckets Aluminium utensils Grinding stones Tyres Flower pots Iron pots Total Container positivity = Number of positive containers divided by total containers searched multiplied by

5 Table.3 Composition of Aedes mosquitoes emerged from different breeding habitats Ae. aegypti Ae.vittatus Ae.albopictus Container type M % F % M % F % M % F % Coconut shells Cement tanks Plastic drums Plastic containers Plastic buckets Aluminium utensils Grinding stones Tires Flower pots Iron pots Total M = Male mosquitoes, F=Female mosquitoes, % = percentage of mosquitoes Table.4 Distribution of collected adult Aedes mosquitoes from different locations in Tirunelveli district. Village name Houses inspected Positive houses (for Ae. sp.) Females collected API Females/house Females/positive house (for Ae. sp.) Puliankudi Sankarankoil Tenkasi Ramaiyanpatti Maruthamputhur Chettiyur Shenkottai Sivagiri Alangulam Panaagudi Surandai Vellanguli Total API = Number of positive houses for adult female Aedes mosquitoes divided by the number of inspected houses multiplied by 100. Regarding the sex ratio of emerged mosquitoes 345 (60.31%) were male and 227 (39.69%) were females (Fig. 3). A total of 56 adult female Aedes mosquitoes were collected from 39 positive houses (Table 4). The composition of adult female collection includes Aedes aegypti 32 (57.14%), Aedes vittatus 20 (35.71%) and Aedes albopictus 4 (7.14%) (Fig 4). As long as larval indices plays vital role in determining the dengue risks, adult density is also related to know the chances of dengue transmission. The API varied from whereas females per house inspected varied from and females per positive house (for Aedes mosquitoes) showed variation from (Table 4). The study shows that the three species of Aedes mosquitoes (both immatures and adults) were abundantly distributed and had expanded their range in all the study areas of Tirunelveli District. Dengue is caused by the Aedes aegypti (principle dengue vector) and Aedes albopictus (secondary vector). 257

3 Sex ratio of emerged mosquito species These vectors lay their eggs in various breeding sources present in and around the human dwellings such as water storage containers (Maciel, 2007).

6 Fig.1 Map showing locations of study areas in Tirunelveli district. Fig. 2 Composition of emerged mosquito species. and other domestic animals. All these water storage practices are favorable to give rise to breeding of Aedes mosquitoes (Swaddiwudhipong et al., 1992) and are closely associated to the spread of dengue infection. Fig. 3 Sex ratio of emerged mosquito species These vectors lay their eggs in various breeding sources present in and around the human dwellings such as water storage containers (Maciel, 2007). The water storage containers constituted the main breeding habitats for Aedes mosquito in Tirunelveli district. Due to poor rainfall and shortage of water supply, the residents of Tirunelveli district stored the water in various containers and the most commonly used water storage containers included plastic drums, cement tanks, plastic containers and aluminium utensils and these containers constituted the major breeding sources in Tirunelveli district (Table 2). The water storage containers remained filled with water and undisturbed for long durations to meet the daily water requirements for diverse purposes of humans M = Male mosquitoes, F = Female mosquitoes. Among various larval indices, house index and container index provides information on the extent of breeding and intensity of breeding respectively. The breteau index combines the information of both the houses and containers, and thus it is an excellent risk indicator of dengue outbreaks (Tun-Lin et al., 1996). Pupal indices are important to know the intensity of transmission and were considered the better and alternate indicator for adult mosquito abundance (Wai et al., 2012). 258

7 Fig. 4 Composition of collected adult Aedes female mosquito population in Tirunelveli district. The adult based density indices are more proper and applicable measures for entomological studies to detect the dengue risk and dengue prone areas because the female mosquitoes are the lone stages which can transmit the dengue virus. Both immatures and adult females of the Aedes mosquitoes were recorded in abundance from the study areas. It is clear that there are many chances of spreading of mild viral infection of dengue among the residents. Thus there is a need of establishment of mosquito control program at Tirunelveli district. Such a program will educate and encourage the community that the effective way to deal with the increasing level of mosquito populations is the source reduction (Dame & Fasulo, 2003) and the Aedes mosquitoes can be controlled by eliminating the water-filled containers to destroy the oviposition sites and all the aquatic stages of Aedes mosquitoes which in turn reduces the chances of spreading of the dengue risks in Tirunelveli district. Acknowledgement The author Mr. Mohd Ayoub Bhat is very thankful to Pondicherry University for providing the financial support. The Director, Vector Control Research Centre (ICMR) also provided great support by making the availability of various institutional facilities. The author is also very gratified to the respected Dr. Ambrose, Entomology division, Xavier college of Pallayamkottai, Tirunelveli, Tamil Nadu for his kind support to complete the study. References Agarwal R., Kapoor S., Nagar R., A. Misra A., Tandon R., Mathur A., Misra A.K., Srivastava K.L., and U. C. Chaturvedi U.C A clinical study of the patients with dengue hemorrhagic fever during the epidemic of 1996 at Lucknow, India. J Trop Med Public. 30: Barraud and Philip James The Fauna of British India, including Ceylon and Burma. Diptera. Vol. 5. Family Culieldae. Tribes Megarhinini and Culicini.Vol. 5. Burkot T. R., Handzel T., Schmaedick M.A., Tufa J., Roberts J.M., and Graves P.M Productivity of natural and artificial containers for Aedes polynesiensis and Aedes aegypti in four American Samoan villages. Med Vet Entomol. 21: Chan, Y. C., Ho B.C., and Chan K.L.1971.Aedes aegypti (L.) and Aedes albopictus (Skuse) in Singapore City: 5. Observations in relation to dengue haemorrhagic fever. Bulletin of the World Health Organ. 44: 651. Dame D., Fasulo T.R Mosquitoes. In: Public health pesticide applicator training manual for USA and its territories. Gainesville: University of Florida. Das B. P., L. Kabilan K., Sharma S.N., Lal S., Regu K., V. K. Saxena V.K Detection of dengue virus in wild caught Aedes albopictus (Skuse) around Kozhikode airport, Malappuram district, Kerala, India. Dengue Bull. l28: Fradin, Mark S., and John F. D Comparative efficacy of insect repellents against mosquito bites.new England Journal of Medicine. 347:

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Entomological investigation and distribution of Aedes mosquitoes in Tirunelveli, Tamil Nadu, India

International Journal of Current Microbiology and Applied Sciences ISSN: 2319-7706 Volume 3 Number 10 (2014) pp. 253-260 http://www.ijcmas.com Original Research Article Entomological investigation and